In digital television broadcasting such as terrestrial digital broadcasting or digital satellite broadcasting, high-definition video signals called Hi-vision video signals are transmitted. Audio signals transmitted in the digital television broadcasting are conformable to stereophonic reproduction called surround. More specifically, such audio signals enable stereophonic reproduction using a 5.1 channel surround system.
A 5.1 channel includes a total of five speakers (five channels) including front (left and right) speakers, a center speaker, and surround (left and right) speakers, and a ultrasonic subwoofer speaker (0.1 channels).
In a home theater system conformable to the 5.1 channel surround system, a digital broadcasting conformable television receiver (hereinafter referred to as a digital television receiving device) having a display screen on a front surface of a user is installed. The front speakers are respectively installed on the right and left sides ahead of a user. The center speaker is arranged on the front surface of the user. The subwoofer speaker is installed in a suitable location ahead of the user. The surround speakers are respectively installed on the right and left sides behind the user.
In order to reproduce audio in the digital television broadcasting using the 5.1 channel surround system, a home theater device having a built-in amplifier is connected to the digital television receiving device via an HDMI cable conforming to a HDMI (High-Definition Multimedia Interface) standard. The HDMI cable includes a data line for transmitting and receiving video/audio data (video data and audio data) and a CEC signal line for transmitting and receiving a CEC (Consumer Electronic Control) command for performing control between devices. The six speakers, described above, are connected to the home theater device.
A method for improving an audio reproduction function using the CEC command conforming to the HDMI standard has conventionally been proposed.
In an audio control system discussed in Patent Document 1, for example, a control signal is transmitted to an AV (Audio Visual) amplifier via an HDMI CEC line depending on whether a headphone is connected to a television receiver. Thus, control is performed depending on whether audio can be output.
In a sound volume correction circuit system discussed in Patent Document 2, a control signal is transmitted from an HDMI compatible STB (Set Top Box) to an HDMI conformable television via an HDMI cable. Thus, an amplification degree of an audio signal of a television is adjusted depending on the type of the STB.
Further, Patent Document 3 discusses an output device to which a plurality of external devices including an HDMI source device are connected. If an HDMI signal input to the HDMI source device does not include an audio signal, a sound volume operation by an operator in the output device is invalidated.    [Patent Document 1] JP 2009-027678 A    [Patent Document 2] JP 2006-352599 A    [Patent Document 3] JP 2009-088646 A